This proposal describes a two-phase intervention and evaluation plan for a school and family-based intervention designed to reduce the prevalence of obesity among American Indian children residing on Indian reservations in the Aberdeen Area of the Indian Health Service. The interventions include school curricula designed to teach skills to limit excessive weight gain through a healthy diet and regular physical activity, modification of the school meals to lower fat and increase complex carbohydrates and also a family-based home component designed to reinforce and support the school program. In addition, there will be reservation grocery store involvement to increase the availability of lower fat food choices, fruits and vegetables. Phase I is proposed as a three-year development phase wherein intervention and evaluation materials and protocols will be developed, pilot-tested and revised, in concert with other Field Centers funded under this RFA. Phase II is proposed as a six-year implementation and evaluation phase wherein the intervention program will be subject to a full field evaluation in elementary schools at each Field Center. Each Field Center will recruit 6-8 elementary schools for a randomized trial with two study conditions, an Intervention Condition and Control Condition. For Phase II, two cohorts of 3rd grade students (2 consecutive classes) will be followed and surveyed annually for four years through the end of their 6th grade year. During their 3rd, 4th, and 5th grade school years, the two cohorts in the Intervention Condition will receive a program of school and family-based intervention activities to modify their eating and physical activity behaviors. The school-based interventions include classroom curricula, physical education program as well as changes in school food service. The family-based intervention includes a home activity program and family nights. The intervention components will be developed with direct input from American Indians through focus groups and interviews during the Needs Assessment phase, as well as continuing input from an American Indian Advisory Council. The primary outcome measures will be changes in the Body Mass Index and the sum of skinfold thicknesses at the triceps and subscapular sites. Secondary outcomes include reduction of dietary fat and excess calories and an increase in moderate to vigorous physical activity. This proposal for Phase I, the planning and feasibility study, will develop and pilot-test the interventions and evaluations on two reservations in South Dakota, the Rosebud Reservation and Pine Ridge Reservation, in one school on each reservation.